Error detected in export .dll - Crystal Reports

When exporting Crystal Reports to a .pdf format, the great error message "Error detected in export .dll" started popping up. It took a while to track down, but the cause was this:
An image field was on the report, but the data was null. Worked fine in the viewer, but just not on the export.
Solution: set "Suppress" to isnull(image_field_here).